Heterogeneous deployment has been considered by the Third Generation Partnership Project (3GPP) Long-Term Evolution-Advanced (LTE-A) working groups as a technique to substantially improve system capacity and coverage. In a heterogeneous deployment, low power network nodes, such as pico evolved Node-Bs (eNBs) and femto eNBs, are overlaid with traditional high power eNBs which can be referred to as macro eNBs. Such macro, pico, and femto eNBs form macro, pico, and femto cells, respectively. The term “cell” refers to an area of coverage of wireless transmission by a network, such as an eNB. In some instances, each of pico cells or femto cells can have a coverage at least partially overlapping with the coverage of the macro cell. To efficiently utilize the radio spectrum, in one embodiment macro, pico and femto cells are deployed on the same carrier. However, full frequency reuse among pico, femto and macro cells could introduce severe inter-cell interference.
In particular, to improve the system capacity, range expansion has been introduced for pico eNBs where a user equipment (UE) could connect to the pico eNB even when the signal from the macro eNB is stronger. Similarly, in closed subscriber group (CSG) femto cells, the UE may receive a stronger signal from the femto cell than from the macro eNB. However, if the UE is not part of the closed subscriber group, the UE may need to connect to the macro eNB. The weaker cell that the UE is connecting to is referred to herein as the victim cell. In such an instance, the stronger cell that the UE is not connecting to can be referred to as the aggressor cell in the context of this document.
One alternative to reduce interference from a victim cell is almost blank sub-frame (ABS) based enhanced inter-cell interference coordination (eICIC). In this alternative, the higher powered cell blanks out transmission or lowers transmitting power on certain sub-frames to enable successful data transmission from the lower powered (victim) cell. However, the almost blank sub frame still contains cell specific reference signals (CRS) and also, if the primary synchronization signal (PSS)/secondary synchronization signal (SSS)/physical broadcast channel (PBCH)/system information block 1 (SIB1)/paging/positioning reference signal (PRS) coincide with the ABS, they are transmitted in the ABS, with the associated physical downlink control channel when SIB1/paging is transmitted.
However, due to the interference from the aggressor cell, the UE may not be able to reliably detect basic signals such as PSS, SSS and PBCH from the weaker cell.
Appendix I is also referred to.